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# cosine

play
noun co·sine \ˈkō-ˌsīn\

## Simple Definition of cosine

• geometry : the ratio between the long side (called the hypotenuse) and the side that is next to an acute angle in a right triangle

Source: Merriam-Webster's Learner's Dictionary

## Full Definition of cosine

1. 1 :  a trigonometric function that for an acute angle is the ratio between the leg adjacent to the angle when it is considered part of a right triangle and the hypotenuse

2. 2 :  a trigonometric function cos θ that for all real numbers θ is given by the sum of the alternating series and that is exactly equal to the cosine of an angle of measure θ in radians

## Origin and Etymology of cosine

New Latin cosinus, from co- + Medieval Latin sinus sine

First Known Use: 1635

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